• International Journal of Human Ecology
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• 제8권2호
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• pp.75-83
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• 2007

Korean secondary school students (n=263) responded to surveys measuring their family contexts and school adjustment during the time period August-September 2004. Structure Equation Modeling tests were conducted to identify the nested model on school adjustment, a latent variable constructed with peer relations, teacher-adolescent relations, and academic attitude. In the nested model, parental involvement was a powerful predictor for school adjustment. Family conflict had a negative impact on school adjustment and was statistically significantly when correlated with the other predictors in the model. These finding suggested that family contexts play an important role in Korean adolescents' school adjustment. Hence, adolescents' perceived GPA level and satisfaction for school were important predictors for school adjustment.

• Nuclear Engineering and Technology
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• 제54권11호
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• pp.4181-4194
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• 2022

Main steam safety valves are commonly used in nuclear power plants to provide final protections from overpressure events. Blowdown and dynamic stability are two critical characteristics of safety valves. However, due to the parameter sensitivity and multi-parameter features of safety valves, using traditional method to design and/or optimize them is generally difficult and/or inefficient. To overcome these problems, a surrogate model-based valve design optimization is carried out in this study, of particular interest are methods of valve surrogate modeling, valve parameters global sensitivity analysis and valve performance optimization. To construct the surrogate model, Design of Experiments (DoE) and Computational Fluid Dynamics (CFD) simulations of the safety valve were performed successively, thereby an ensemble surrogate model (E-AHF) was built for valve blowdown and stability predictions. With the developed E-AHF model, global sensitivity analysis (GSA) on the valve parameters was performed, thereby five primary parameters that affect valve performance were identified. Finally, the k-sigma method is used to conduct the robust optimization on the valve. After optimization, the valve remains stable, the minimum blowdown of the safety valve is reduced greatly from 13.30% to 2.70%, and the corresponding variance is reduced from 1.04 to 0.65 as well, confirming the feasibility and effectiveness of the optimization method proposed in this paper.

• Journal of Information Processing Systems
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• 제15권3호
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• pp.570-592
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• 2019

The Event-B design pattern is an excellent way to quickly develop a formal model of the system. Researchers have proposed a number of Event-B design patterns, but they all lack formal behavior semantics. This makes the analysis, verification, and simulation of the behavior of the Event-B model very difficult, especially for the control-intensive systems. In this paper, we propose a novel method to transform the Event-B synchronous control flow design pattern into the labeled transition system (LTS) behavior model. Then we map the design pattern instantiation process of Event-B to the instantiation process of LTS model and get the LTS behavior semantic model of Event-B model of a multi-level complex control system. Finally, we verify the linear temporal logic behavior properties of the LTS model. The experimental results show that the analysis and simulation of system behavior become easier and the verification of the behavior properties of the system become convenient after the Event-B model is converted to the LTS model.

• 한국과학교육학회지
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• 제29권1호
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• pp.1-9
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• 2009

본 연구에서는 중학교 과학교과서에서 많이 제시되는 과학 개념 모형에 대해 학생들로 하여금 단순히 읽고 지나가는 것이 아니라 주목하고 분석해 보는 시간을 갖게 하는 것이 과학 개념 학습에 어떠한 영향을 미치는지를 조사하였다. 과학 개념 모형에 좀 더 주목하고 분석해 보게 하는 방법으로 본 연구에서는 미완성 과학 개념 완성 활동과 과학 개념 모형 수정 활동을 고안하였으며, 이들 활동을 전통적 수업활동과 비교하였다. 연구 대상으로는 B광역시 소재 1개 중학교 3학년 학생 112명(3개 학급)을 표집하였다. 이렇게 표집한 3개 학급은 각각 미완성 개념 모형을 완성하는 활동, 주어진 개념 모형을 수정하는 활동, 전통적인 과학 수업 활동을 하도록 하고 그 성취도를 비교하였다. 본 연구의 결과는 첫째, 미완성 과학 개념 모형 완성활동은 전통적 과학 수업 활동에 배해 중학생들의 과학개념 학습에 효과적이라고 할 수 있다. 또한, 개념 모형 완성 활동을 통한 성취도는 학생들의 학교 성적이 높을수록 높고, 학생들의 인지 수준이 구체적 조작 단계에 있는 학생이거나 과도기에 있는 학생들이 높다. 둘째, 과학 개념 모형의 수정 활동은 전통적 과학수업 활동에 비해 중학생들의 과학 개념 학습에 효과적이라고 말하기 어렵다. 또한, 과학 개념 모형의 수정활동을 통한 성취도는 학생들의 학교 성적이 높을수록 높기는 하지만 하위 수준 학생들의 경우에는 수업 후 성취도가 높아지지 않음을 볼 때 개념 모형 수정 활동은 중학생 수준에는 적합하지 않다고 할 수 있다. 셋째, 중학교 학생들의 경우에는 미완성 과학 개념 모형의 완성 활동을 통한 수업이 과학 개념 모형 수정 활동을 통한 수업에 비해 개념 학습에 효과적이다.

• Journal of applied mathematics & informatics
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• 제30권3_4호
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• pp.489-498
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• 2012

Most of the software reliability models are based on black box approach and these models consider the entire software system as a single unit. Present day software development process has changed a lot. In present scenario these models may not give better results. To overcome this problem an improved additive model has been proposed in this paper, to estimate the reliability of software with modular structure. Also the concept of imperfect debugging has been also considered. A maximum likelihood estimation technique has been used for estimating the model parameters. Comparison has been made with an existing model. ${\chi}^2$ goodness of fit has been used for model fitting. The proposed model has been validated using real data.

• Structural Engineering and Mechanics
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• 제26권4호
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• pp.377-392
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• 2007

A discrete sliding mode control (SMC) method based on hybrid model of neural network and nominal model is proposed to reduce the vibration of flexible structures, which is a robust active controller developed by using a sliding manifold approach. Since the thick boundary layer will reduce the virtue of SMC, the multilayer feed-forward neural network is adopted to model the uncertainty part. The neural network is trained by Levenberg-Marquardt backpropagation. The design objective of the sliding mode surface is based on the quadratic optimal cost function. In course of running, the input signal of SMC come from the hybrid model of the nominal model and the neural network. The simulation shows that the proposed control scheme is very effective for large uncertainty systems.

• Transactions on Control, Automation and Systems Engineering
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• 제2권4호
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• pp.221-227
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• 2000

This paper combines the constrained model predictive control with the feedback linearization to solve a nonlinear system control problem with input constraints. The combined approach consists of two steps: Firstly, the nonlinear model is linearized by the feedback linearization. Secondly, based on the linearized model, the constrained model predictive controller is designed taking input constraints into consideration. The proposed controller is applied to two link robot system, and tracking performances of the controller are investigated via some simulations, where the comparisons are done for the cases of unconstrained, constrained input in feedback linearization.

• International Journal of Aeronautical and Space Sciences
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• 제16권1호
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• pp.64-76
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• 2015

This paper suggests applying pseudospectral model predictive method for exo-atmospheric guidance. The method is a fusion of pseudospectral law and model predictive control, in which a two point boundary value problem is formulated using model predictive approach and solved by applying pseudospectral law. In this work, the method is applied to exo-atmospheric guidance with specific target requirement. The existing exo-atmospheric guidance methods suffice general requirements for guidance, but cannot ensure specific target constraints; whereas, the presented method is able to do so. The proposed guidance law is assessed through simulation of perturbed cases, and the tests suggest that the method is able to operate semi-autonomously under control and thrust vector perturbations.

• Journal of international Conference on Electrical Machines and Systems
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• 제2권3호
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• pp.260-268
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• 2013

Based on classical Berotti discrete iron loss calculation model, the iron loss analysis mathematical model of alternator was proposed in this paper. Considering characteristics of high speed and changing frequency of the alternator, Maxwell 3-D model was built to analyze iron loss corresponding to each running speed in alternator. Based on iron loss model of alternator at rated speed, the rotor claw pole size was made an optimization design. The optimization results showed that alternator's output performance had been improved. A new idea was explored in size optimization design of claw pole alternator.

• Computers and Concrete
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• 제11권4호
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• pp.291-304
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• 2013

By considering the creep characteristics of concrete core under eccentric compression, a creep model of concrete filled steel tubes (CFT) columns under eccentric compressive loads is proposed based on the concrete creep model B3. In this proposed model, a discrete element method is introduced to transform the eccentric loading into axial loading. The validity of the model is verified by comparing the predicting results with the published creep experiments results on CFT specimens under compressive loading, together with the predicting values based on other concrete creep models, such as ACI209, CEB90, GL2000 and elastic continuation and plastic flow theory. By using the proposed model, a parameters study is carried out to analysis the effects of practical design parameters, such as concrete mix (e.g. water to cement ratio, aggregate to cement ratio), steel ratio and eccentricity ratio, on the creep of CFT columns under eccentric compressive loading.